1. Field of the Invention
The present invention relates to a device for locating easily and with great accuracy tomodensitometric sections made on a subject to be examined, this location being made in relation to conventional and predetermined anatomic planes of a subject.
2. Description of the Prior Art
Tomodensitometry apparatus are now well-known and will not be described here. It is sufficient for understanding the subject matter of the present invention to know that, whatever the type of tomodensitometry contemplated, it enables images to be obtained of the different slices of the patient examined. These slices of examination, called tomodensitometric sections, are generally perpendicular to the longitudinal axis (or great axis) of the subject to be examined. They may however be sloping with respect to this axis. This is particularly the case when it is a matter of producing tomodensitometric sections of the head. In this case the sections may be parallel to the orbito-meatal plane, i.e. in a plane slightly inclined with respect to the plane normal to the longitudinal axis of the patient; they may also be parallel to the frontal plane of the subject, i.e. perpendicular to the above-described sections.
It may be further useful in some cases to have sections inclined with respect to the different planes which have just been defined.
It is conventional to equip tomodensitometers with locating devices which enable the operator to recognize the sections which he is making, not only in relation to each other, but in relation to the anatomy of the patient examined.
There exist at present different types of locating devices; two of these types of devices are briefly recalled here.
U.S. Pat. No. 4,117,337 describes a locating device using light centering which, from previous relatively complex adjustments, enable a plane to be defined on the subject to be examined which will be the reference plane. All the sections subsequently made will be located with respect to this reference plane. Such a system presents, besides its complexity, different drawbacks. On the one hand it requires previous adjustment which is relatively time consuming to achieve. Defining a reference plane which is not tied to the subject to be examined but to the optical centering device requires practically absolute immobility of the patient at the risk of losing all efficiency, and must be redone for each new examination, which is a considerable disadvantage.
Another type of locating device is described in U.S. Pat. No. 4,115,691. This device, much simpler than the preceding one, includes in a small cylinder which is placed against the subject to be examined. This small cylinder includes different juxtaposed portions along the different sections to be effected. Each portion includes a number which will be visualized in the tomodensitometric image and which enables the different sections to be identified in relation to each other. This device, though it is much simpler than the preceding one, presents however certain drawbacks. It is in fact indispensable for the sections to be perpendicular to the cylinder containing the locating numbers. Furthermore, the first section must be suitably positioned with respect to this cylinder, so as not to be astride two adjacent portions, which would make the reading of the two numbers impossible. Such a device requires then previous adjustment of the first section with respect to the length of the small cylinder. Moreover, it does not enable sections to be made at any angle of incidence.